Control of line-to-line overvoltages for helicopter-based live work on a 500 kV transmission line

Transient overvoltage protection during live maintenance of high voltage transmission lines is necessary to prevent line-line sparkovers due to possible transient overvoltages. Portable protective air gaps(PPAGs) along a transmission line under maintenance are proposed to limit the line-ground voltage transients. Previous work has shown that a 41 inch rod gap installed along the line for sparkover protection will provide protection at approximately 1.7 per unit on a 500 kV system. The PPAG had not previously been used to provide protection line-line, however. This paper presents the results from a study that confirms whether PPAGs installed line-ground could also provide adequate protection from line-line overvoltages, and to determine the optimal installation scheme of sets of PPAGs over the length of the line or line section.